A room leading into a large room or hall

Answer: Option A

One word substitute is Anteroom.

Anteroom: an antechamber, typically serving as a waiting room.
Lounge: lie, sit, or stand in a relaxed or lazy way.
Lobby: a room providing a space out of which one or more other rooms or corridors lead, typically one near the entrance of a public building.
Pantry: a small room or cupboard in which food, crockery, and cutlery are kept.